When light crosses from air into glass it slows down — and a beam that hits at an angle has to bend toward the normal. Don't take our word for it. Grab the ray below and move it around.
Try it — drag the incident ray
sim · Air → GlassDRAG THE RAY
Angle of incidence42°
Angle of refraction26.5°
sin i / sin r1.50
Notice the refracted angle is always smaller than the incident angle — and the ratio sin i / sin r stays ≈ 1.5 no matter how you move it. You just found a law.
You discovered · Snell's law
n₁ sin i = n₂ sin r
That constant ratio is the refractive index of glass, n = 1.5.
Quick check
If you keep increasing the angle of incidence, the refracted ray…
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